Compass bowl



May 18, 1943 E. F. BRITTEN, JR 2,319,529

COMPASS BOWL Filed Jan. 23, 1943 aha-7 4.1

INVENTOR ORNEY Patented May 18, 1943 COMPASS BOWL Edwin F. Britten, Jr., Short Hills, N. J., assignor to Monroe Calculating Machine Company, Orange, N. 1., a corporation of Delaware Application January 23, 1943, Serial No. 473,354

1 Claim.

The invention has relation to bowls for magnetic compasses and it consists in the novel construction and combination of parts as set forth in the appended claim.

In the accompanying drawing, illustrating the invention Fig. 1 is a vertical section through the compass.

bowl and associated parts of a magnetic compass.

Fig. 2 is a plan view of the bowl and the photoelectric devices used in the compass.

The bowl is intended for use in connection with a magnetic compass provided with follower mechanism controlled by photo-electric devices, as shown, for instance in the copending application for patent filed by the present applicant of even date herewith.

The photo-electric control devices comprise a I source of light l9 mounted within a closure having a vertical slot 2| in its inner wall, light from source l9 passing through slot 2|, through the glass of the compass bowl l0 and the liquid with which the bowl is filled, and striking a mirror It fixed upon the frame which carries the compass needle I3. The closure 20, together with the photo-electric tubes to be described are carried on a rotary plate mounted within the compass casing, and upon rotary driven movement of the plate, as modified by turning movement of the conveyance in which the compass is mounted, the parts carried upon the plate will move relatively to the compass needle and mirror ll, so that the light reflected from this mirror will strike one of two mirrors 23, 24, angularly disposed upon the wall of the closure 20 one at either side of slot 2|, as shown in Fig. 2, and will be reflected therefrom to one or the other of two photo-electric tubes 25, 26. The follower devices will keep the plate rotating first in one and then in the other direction,as controlled by the tubes 25, 26, in known manner, so that the source of light will be carried around the compassbowl in following relative movement of the needle.

It be apparent that the beam of light should be accurately reflected and not bent due to irregularities" 'of the glass surface through which it passes. It is intended that the compass bowl shall be filled with kerosene or other liquid 7 having substantially :the same index of refraction as the material of the bowl, and hence it is ISO not necessary that the interior surface of the bowl be optically true. However, the portion of the exterior surface through which the light enters and leaves the bowl must be optically true in order to prevent bending of the rays of light, and for this purpose it is intended that it should be ground and polished.

In order that the light beam may not be interrupted at any time by the posts of a supporting frame, it is intended to secure the compass bowl in position from the upper closure plate I I thereof by means of clamps l2. Hence the upper margin of the bowl is formed with a flange 68, with the under surface of which clamps l2 engage. Another advantage of this method of suspension lies in the small vertical dimension of the flange, giving less expansion and contraction.

The application of an upper flange to compass bowls of known construction would make it difllcult to grind the circumferential surface of the bowl, since it is preferable that the grinding tool be reciprocated during the operation, so that every point of the grinding surface shall contact every point of the ground surface. Hence the flange 68 would be in the way. This interference cannot be avoided .by elongating the upper portion of the bowl, since magnetic compasses are customarily provided with compensating devices, mounted above the bowl and in as close proximity as possible to the needle of the compass. Thus the flange 68 will not be spaced above the ground surface by an interval as great as the depth of said surface.

These conditions are met by forming the bowl with an annular projecting central band 69, having a vertical outer face of a diameter equal to or greater than that of flange 68, whereby there will be nothing to interfere with the grindin tool in imparting an optically true surface tothis outer face.

I claim:' I

A glass compass bowl characterized by'acylindrical wall formed with an upper clamping flange and an annular projecting central band of greater depth than the interval between the band and the flange and having a vertical ground outer face of a diameter not less than that of said flange.

EDWIN F. BRITTEN, JR. 

